In Colorado, 18.7 percent of adults are obese — making it the only state with an adult obesity rate under 20 percent. Meanwhile, 33.5 percent of West Virginian adults are obese, the poll found.

The national obesity rate sits near the middle of those extremes, at 26.2 percent in 2012, hardly changed from the 2011 rate of 26.1 percent. In fact, all but four states in 2012 had obesity rates that were not statistically different from 2011. Waistlines widened in New Jersey, Georgia and North Carolina, while Delaware got skinnier, Gallup found.

The results come from the Gallup-Healthways Well-Being Index survey, in which 353,564 randomly selected adults in all 50 states were interviewed between Jan. 1 and Dec. 31, 2012. Participants reported their height and weight, which was used to calculate body mass index, or BMI, a measure of a person's body fatness. BMI scores of 30 or greater are considered obese. (For example, a 5-foot-4-inch woman who weighs 174 pounds or more, or a 5-foot-10-inch man who weighs 209 pounds or more would have a BMI of 30 or over.)

Obesity puts individuals at risk of a slew of other conditions, including Type 2 diabetes, high blood pressure and sleep problems, and the survey results support those links. Colorado had the lowest rate of adults diagnosed with high blood pressure (22 percent), with Minnesota (23.8 percent) and Wyoming (24.6 percent) close behind. West Virginia had the highest rate of adults with high blood pressure (39.7 percent), followed by Mississippi (38.4 percent) and Alabama (36.4 percent), Gallup found.

The three states with the lowest diabetes rates were Alaska (6.0 percent), Colorado (7.4 percent) and Montana (8.1 percent), whereas the three states with the highest rates were Mississippi (15.4 percent), West Virginia (15.2 percent) and Alabama (13.6 percent).

"With obesity rates up in nearly all age groups since 2008, it is a problem that requires the nation's attention," Gallup officials wrote in their report. "The economic impact to the U.S. carries a heavy cost — the Centers for Disease Control and Prevention reports that obesity alone costs about $147 billion annually."